Abstract
At stress intensity factor ranges near the threshold for fatigue crack propagation, the size of the cyclic plastic zone is very small. Hence, size effects in the plasticity have to be taken into account. Discrete dislocation mechanics is an appropriate tool to analyze the consequences of the discrete nature of plasticity. A short overview of the different types of performed discrete dislocation simulations of cyclically loaded cracks and their essential results are presented. Discrete dislocation mechanics deliver the changes of the stresses and displacements during cyclic loading. The crack propagation rate depends thereby on the underlying propagation mechanism. Two types of simulations are presented here. For ductile materials a blunting and re-sharpening mechanism is assumed, i.e., the crack propagation rate is direct proportional to the cyclic crack tip opening displacement. For plastically deformable brittle materials, a propagation by decohesion induced by the applied stress and the induced stress fields of the dislocations are assumed. Both simulations deliver a clear threshold of stress intensity factor range in similar order of magnitude and a good agreement of the experimental observed propagation behavior in the near threshold of stress intensity factor range regime.
Published Version
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